Hornbeck offers Rachel the apple but she refuses. He then says that he is not the serpent which means that he won't turn Rachel evil. Little Eva is another name for Rachel that he gave her. In the Old Testament, the snake offered Adam and Eve an apple from the Tree of Knowledge. Because they ate the apple, sin was introduced into the world. By saying that there is no Tree of Knowledge, he is saying that there are no sins or temptations in Heavenly Hillsboro.